Another double-edged knife. Amazing things can happen if this data is used wisely. I don't even think what could happen if this data falls into the wrong hands though.
Agreed, so the question then becomes "how likely is the data to be used responsibly?"
... and I'll leave it at that.
From the point of view of providing preventive medicine and lowering overall healthcare costs, this is the right way. From the point of view of this info being used by insurance companies, not so good.